Incidence of Underlying Abnormal Findings on Routine Magnetic Resonance Imaging for Bell Palsy.

Importance: There is no consensus on the benefits of routine magnetic resonance imaging (MRI) of the facial nerve in patients with suspected idiopathic peripheral facial palsy (PFP) (ie, Bell palsy [BP]). Objectives: To estimate the proportion of adult patients in whom MRI led to correction of an initial clinical diagnosis of BP; to determine the proportion of patients with confirmed BP who had MRI evidence of facial nerve neuritis without secondary lesions; and to identify factors associated with secondary (nonidiopathic) PFP at initial presentation and 1 month later. Design, Setting, and Participants: This retrospective multicenter cohort study analyzed the clinical and radiological data of 120 patients initially diagnosed with suspected BP from January 1, 2018, to April 30, 2022, at the emergency department of 3 tertiary referral centers in France. Interventions: All patients screened for clinically suspected BP underwent an MRI of the entire facial nerve with a double-blind reading of all images. Main Outcomes and Measures: The proportion of patients in whom MRI led to a correction of the initial diagnosis of BP (any condition other than BP, including potentially life-threating conditions) and results of contrast enhancement of the facial nerve were described. Results: Among the 120 patients initially diagnosed with suspected BP, 64 (53.3%) were men, and the mean (SD) age was 51 (18) years. Magnetic resonance imaging of the facial nerve led to a correction of the diagnosis in 8 patients (6.7%); among them, potentially life-threatening conditions that required changes in treatment were identified in 3 (37.5%). The MRI confirmed the diagnosis of BP in 112 patients (93.3%), among whom 106 (94.6%) showed evidence of facial nerve neuritis on the affected side (hypersignal on gadolinium-enhanced T1-weighted images). This was the only objective sign confirming the idiopathic nature of PFP. Conclusions and Relevance: These preliminary results suggest the added value of the routine use of facial nerve MRI in suspected cases of BP. Multicentered international prospective studies should be organized to confirm these results.